Reversible tuning of magnetocaloric Ni-Mn-Ga-Co films on ferroelectric PMN-PT substrates

TL;DR

This study demonstrates reversible tuning of magnetization in Ni-Mn-Ga-Co thin films on ferroelectric substrates via electric field-induced strain, enabling control of magnetic properties for magnetocaloric applications.

Contribution

It shows that electric field-induced strain in ferroelectric substrates can reversibly modify the magnetic properties of magnetocaloric Ni-Mn-Ga-Co films, without changing the transformation temperature.

Findings

Reversible change of magnetization within the austenitic state.

Strain transfer from ferroelectric substrate to thin film confirmed by X-ray diffraction.

No change observed in martensitic transformation temperature.

Abstract

Tuning functional properties of thin caloric films by mechanical stress is currently of high interest. In particular, a controllable magnetisation or transition temperature is desired for improved usability in magnetocaloric devices. Here, we present results of epitaxial magnetocaloric Ni-Mn-Ga-Co thin films on ferroelectric Pb(Mg$_{1/3}$Nb$_{2/3}$)$_{0.72}$Ti$_{0.28}$O$_3$ (PMN-PT) substrates. Utilizing X-ray diffraction measurements, we demonstrate that the strain induced in the substrate by application of an electric field can be transferred to the thin film, resulting in a change of the lattice parameters. We examined the consequences of this strain on the magnetic properties of the thin film by temperature and electric field dependent measurements. We did not observe a change of martensitic transformation temperature but a reversible change of magnetisation within the austenitic state, which we attribute to the intrinsic magnetic instability of this metamagnetic Heusler alloy.